YARN-6323. Rolling upgrade/config change is broken on timeline v2. (Vrushali C via Haibo Chen)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/conf/YarnConfiguration.java

@@ -2221,6 +2221,8 @@ public class YarnConfiguration extends Configuration {
 
   public static final int DEFAULT_NUMBER_OF_ASYNC_ENTITIES_TO_MERGE = 10;
 
+  /** default version for any flow. */
+  public static final String DEFAULT_FLOW_VERSION = "1";
 
   /**
    * The time period for which timeline v2 client will wait for draining

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/ContainerManagerImpl.java

@@ -402,6 +402,16 @@ public class ContainerManagerImpl extends CompositeService implements
         LOG.debug(
             "Recovering Flow context: " + fc + " for an application " + appId);
       }
+    } else {
+      // in upgrade situations, where there is no prior existing flow context,
+      // default would be used.
+      fc = new FlowContext(TimelineUtils.generateDefaultFlowName(null, appId),
+          YarnConfiguration.DEFAULT_FLOW_VERSION, appId.getClusterTimestamp());
+      if (LOG.isDebugEnabled()) {
+        LOG.debug(
+            "No prior existing flow context found. Using default Flow context: "
+                + fc + " for an application " + appId);
+      }
     }
 
     LOG.info("Recovering application " + appId);